Method and system for measuring the cardiac output of a living being

Abstract

A system is provided for use in measuring the cardiac output of a living being. The system includes at least one sensor for measuring the lung carbon dioxide elimination rate of the living being and a processor for predicting the cardiac ouput level of the living being as a function of the current value of the lung carbon dioxide elimination rate based upon the predictive increase in cardiac output as the lung carbon dioxide elimination rate of the living being increases. Structure is provided for determining the cardiac ouput of an intubated living being and a non-intubated living being.

What is claimed is: 
     
       1. A method for determining a cardiac output level of a patient, the method comprising: (a) monitoring the carbon dioxide production of the patient to obtain a current value of the lung carbon dioxide elimination rate of the patient; and   (b) predicting the cardiac output level of the patient as a function of the current value of the carbon dioxide elimination rate, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide rate increases.   
     
     
       2. The method of claim 1, wherein the monitoring step comprises the steps of: (i) sensing a flow rate of the exhaled gas expired by the patient and generating a flow signal representative of the flow rate;   (ii) sensing a carbon dioxide level of the exhaled gas expired by the patient and generating a carbon dioxide signal representative of the carbon dioxide level; and   (iii) processing the flow signal and the carbon dioxide signal to determine the current value of the lung carbon dioxide elimination rate of the patient.   
     
     
       3. The method of claim 2, wherein the flow rate sensing step comprises continuously measuring the flow rate of exhaled gas during an exhalation effort by the patient. 
     
     
       4. The method of claim 2, wherein the carbon dioxide level sensing step comprises continuously sensing the carbon dioxide level of the exhaled gas during an exhalation effort by the patient. 
     
     
       5. The method of claim 2, wherein the step of generating the flow signal further comprises the step of converting the flow signal to a digitized flow signal. 
     
     
       6. The method of claim 2, wherein the step of generating the carbon dioxide signal further comprises the step of converting the carbon dioxide signal to a digitized carbon dioxide signal. 
     
     
       7. The method of claim 2, wherein the step of processing comprises the steps of: (A) extracting a measured exhaled volume of the exhaled gas from the flow signal;   (B) storing a set of curve data representative of the sensed carbon dioxide level of the exhaled breathing gas as a function of the measured exhaled volume of the gas; and   (C) integrating the set of curve data over a time interval to determine the current value of the lung carbon dioxide elimination rate of the patient.   
     
     
       8. The method of claim 7, wherein the time interval is one minute. 
     
     
       9. The method of claim 1, further comprising the step of displaying the cardiac output level. 
     
     
       10. The method of claim 9, wherein the step of displaying comprises the step of visually displaying the cardiac output level corresponding to the determined carbon dioxide elimination rate of the patient. 
     
     
       11. The method of claim 9, wherein the step of displaying comprises the step of recording the cardiac output level corresponding to the determined carbon dioxide elimination rate of the patient. 
     
     
       12. The method of claim 2, wherein the step of measuring the flow rate of the exhaled gas comprises measuring the flow rate of the exhaled gas in at least one location in a flow path of the exhaled gas. 
     
     
       13. The method of claim 2, wherein the step of sensing the carbon dioxide level of the exhaled gas comprises sensing the carbon dioxide level of the exhaled gas in at least one location in a flow path of the exhaled gas. 
     
     
       14. The method of claim 2, further comprising providing the patient with a breathing attachment having a proximal end, a distal end, and a breathing channel extending therethrough from the proximal end to the distal end, the distal end of the breathing attachment in flow communication with the lungs of the patient such that a flow path of the exhaled gas passes through the breathing channel, wherein the step of measuring the flow rate of the exhaled gas comprises measuring the flow rate of the exhaled gas in the flow path of the exhaled gas near the proximal end of the breathing attachment, and wherein the step of sensing the carbon dioxide level of the exhaled gas comprises sensing the carbon dioxide level of the exhaled gas in the flow path of the exhaled gas near the proximal end of the breathing attachment. 
     
     
       15. The method of claim 1, wherein the step of predicting comprises the steps of: (i) selecting the predictive relationship appropriate for the patient, wherein a first predictive relationship is selected for ill patients and a second predictive relationship is selected for healthy patients; and   (ii) determining the cardiac output level based on the selected predictive relationship and the current value of the lung carbon dioxide elimination rate of the patient.   
     
     
       16. A system for determining a cardiac output level of a patient, comprising: means for monitoring the lung carbon dioxide elimination rate of the patient which is representative of the volume of carbon dioxide expired by the patient per unit time;   processing means responsive to the carbon dioxide elimination rate monitoring means for determining a current value for the carbon dioxide elimination rate of the patient; and   predicting means for determining the cardiac output level of the patient based on the determined current value of the current value of the carbon dioxide elimination rate, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases.   
     
     
       17. The system of claim 16, wherein the monitoring means is comprised of means for sensing the flow rate of the exhaled gas expired by the patient and means for sensing the carbon dioxide level of the exhaled gas expired by the patient. 
     
     
       18. The system of claim 17, wherein the processing means includes means responsive to the flow rate sensed by the flow rate sensing means for providing the measured volume of the exhaled gas expired by the patient during an exhalation effort of the patient. 
     
     
       19. The system of claim 18, wherein said processing means is responsive to the measured volume of the exhaled gas and the carbon dioxide level sensed by the carbon dioxide sensing means for determining the current value of the carbon dioxide elimination rate of the patient. 
     
     
       20. The system of claim 17, wherein the flow rate sensing means and the carbon dioxide sensing means are disposed in a flow path of the exhaled gas. 
     
     
       21. The system of claim 20, further comprising a breathing attachment having a proximal end, a distal end, and a breathing channel extending therethrough from the proximal end to the distal end, the distal end of the breathing attachment in flow communication with the lungs of the patient such that the flow path of the exhaled gas passes through the breathing channel, wherein the flow rate measuring means and the carbon dioxide sensing means are disposed in the flow path of the exhaled gas near the proximal end of the breathing attachment. 
     
     
       22. The system of claim 16, further comprising display means, coupled to the predicting means, for displaying the measurement of the cardiac output level of the patient to an operator of the system. 
     
     
       23. The system of claim 16, wherein the predicting means includes means for selecting a predictive relationship appropriate for the patient, wherein a first predictive relationship is selected for ill patients and wherein a second predictive relationship is selected for healthy patients. 
     
     
       24. The system of claim 23, wherein the predicting means includes means for determining the cardiac output of the patient based on the selected predictive relationship and the determined current value of the carbon dioxide elimination rate. 
     
     
       25. The system of claim 16, further comprising storage means, coupled to the processing means and the predicting means, for storing the current value of the lung carbon dioxide elimination rate and the determined cardiac output level. 
     
     
       26. A system for determining a cardiac output level of a patient from the carbon dioxide elimination rate of the patient, the system comprising: a flow rate sensor which measures a flow rate of the exhaled gas expired by the patient and which provides a flow signal representative of the flow rate;   a carbon dioxide sensor which senses a carbon dioxide level of the exhaled gas expired by the patient and which provides a carbon dioxide signal representative of the carbon dioxide level; and   a processor which: receives the carbon dioxide signal and the flow signal;   determines a current value of lung carbon dioxide elimination rate of the patient from the carbon dioxide signal and the flow signal; and   predicts the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate of the patient, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases.     
     
     
       27. The system of claim 26, wherein the processor extracts a measured volume of exhaled gas from the flow signal and wherein the processor determines the current value of lung carbon dioxide elimination rate from the carbon dioxide signal and the measured volume. 
     
     
       28. The system of claim 26, further comprising a first digitizer which receives the flow signal from the flow rate sensor and converts the flow signal into a digitized flow signal which is received by the processor. 
     
     
       29. The system of claim 26, further comprising a second digitizer which receives the carbon dioxide signal and converts the carbon dioxide signal into a digitized carbon dioxide signal which is received by the processor. 
     
     
       30. The system of claim 26, wherein the flow rate sensor senses the flow of the exhaled gas continuously during an exhalation effort of the patient. 
     
     
       31. The system of claim 26, wherein the carbon dioxide sensor senses the carbon dioxide level of the exhaled gas continuously during the exhalation effort of the patient. 
     
     
       32. The system of claim 26, further comprising a display device which receives the cardiac output level from the processor and displays that level. 
     
     
       33. The system of claim 32, wherein the display device comprises a monitor which visually displays the cardiac output level. 
     
     
       34. The system of claim 32, wherein the display device is a recorder which records the cardiac output level. 
     
     
       35. The system of claim 26, wherein the flow rate sensor and the carbon dioxide sensor are disposed in a flow path of the gas expired by the patient. 
     
     
       36. The system of claim 35, further comprising a breathing attachment having a proximal end, a distal end, and a breathing channel extending therethrough from the proximal end to the distal end, the distal end of the breathing attachment in flow communication with the lungs of the patient such that the flow path of the exhaled gas passes through the breathing channel, wherein the flow rate measuring sensor and the carbon dioxide sensor means are disposed in the flow path of the exhaled gas near the proximal end of the breathing attachment. 
     
     
       37. The system of claim 35, wherein the carbon dioxide sensor is a capnometer. 
     
     
       38. The system of claim 35, wherein the flow rate measurement sensor is a pneumotachometer. 
     
     
       39. The system of claim 26, further comprising an input device operatively coupled to the processor. 
     
     
       40. The system of claim 39, wherein a first predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate for ill patients may be selected by an operator via the input device, and wherein a second predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate for for healthy patients may be selected by an operator via the input device, so that the processor uses the selected first or second predictive relationship to predict the cardiac output level of the patient based on the relative respiratory health of the patient. 
     
     
       41. A system for determining a cardiac output level of a patient from the carbon dioxide elimination rate of the patient, the system comprising: a flow rate measurement sensor which measures the flow rate of the exhaled gas expired by the patient and which provides a flow signal representative of that flow rate;   a carbon dioxide sensor which senses the carbon dioxide level of the exhaled gas expired by the patient and which provides a carbon dioxide signal representative of that carbon dioxide level;   a first processor which receives the carbon dioxide signal and the flow signal, and determines a current value of the lung carbon dioxide elimination rate of the patient from the carbon dioxide signal and the flow signal and which generates a lung carbon dioxide elimination rate signal representative of the current value of the lung carbon dioxide elimination rate; and   a second processor which receives the lung carbon dioxide elimination rate signal and, based on the current value of that signal, predicts the cardiac output level of the patient, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases.   
     
     
       42. The system of claim 41, wherein the flow rate sensor senses the flow of the exhaled gas continuously during an exhalation effort of the patient. 
     
     
       43. The system of claim 41, wherein the carbon dioxide sensor senses the carbon dioxide level of the exhaled gas continuously during the exhalation effort. 
     
     
       44. The system of claim 41, further comprising a display device which receives the cardiac output level from the second processor and displays that level. 
     
     
       45. The system of claim 41, wherein the flow rate sensor and the carbon dioxide sensor are disposed in a flow path of the gas expired by the patient. 
     
     
       46. The method of claim 45, further comprising a breathing attachment having a proximal end, a distal end, and a breathing channel extending therethrough from the proximal end to the distal end, the distal end of the breathing attachment in flow communication with the lungs of the patient such that the flow path of the exhaled gas passes through the breathing channel, wherein the flow rate measuring sensor and the carbon dioxide sensor are disposed in the flow path of the exhaled gas near the proximal end of the breathing attachment. 
     
     
       47. The system of claim 41, further comprising an input device operatively coupled to the second processor. 
     
     
       48. The system of claim 47, wherein a predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate may be selected by an operator via the input device, wherein a first predictive relationship is selected for ill patients and a second predictive relationship is selected for healthy patients so that the second processor predicts the cardiac output level based on the relative respiratory health of the patient. 
     
     
       49. A method for determining a cardiac output level of a patient, the method comprising: (a) monitoring the carbon dioxide production of the patient to obtain a current value of the lung carbon dioxide elimination rate of the patient by: (i) sensing a flow rate of the exhaled gas expired by the patient and generating a flow signal representative of the flow rate;   (ii) sensing a carbon dioxide level of the exhaled gas expired by the patient and generating a carbon dioxide signal representative of the carbon dioxide level; and   (iii) processing the flow signal and the carbon dioxide signal to determine the current value of the lung carbon dioxide elimination rate of the patient by: (A) extracting a measured exhaled volume of the exhaled gas from the flow signal;   (B) storing a set of curve data representative of the sensed carbon dioxide level of the exhaled breathing gas as a function of the measured exhaled volume of the gas; and   (C) integrating the set of curve data over a time interval to determine the current value of the lung carbon dioxide elimination rate of the patient; and       (b) predicting the cardiac output level of the patient as a function of the current value of the carbon dioxide elimination rate, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide rate increases.   
     
     
       50. The method of 49, wherein the time interval is one minute. 
     
     
       51. A method for determining a cardiac output level of a patient, the method comprising: (a) monitoring the carbon dioxide production of the patient to obtain a current value of the lung carbon dioxide elimination rate of the patient; and   (b) predicting the cardiac output level of the patient as a function of the current value of the carbon dioxide elimination rate by: (i) selecting the predictive relationship appropriate for the patient, wherein a first predictive relationship is selected for ill patients and a second predictive relationship is selected for healthy patients; and   (ii) determining the cardiac output level based on the selected predictive relationship and the current value of the lung carbon dioxide elimination rate of the patient, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide rate increases.       
     
     
       52. A system for determining a cardiac output level of a patient, comprising: means for monitoring the lung carbon dioxide elimination rate of the patient which is representative of the volume of carbon dioxide expired by the patient per unit time;   processing means responsive to the carbon dioxide elimination rate monitoring means for determining a current value for the carbon dioxide elimination rate of the patient; and   predicting means for determining the cardiac output level of the patient based on the determined current value of the current value of the carbon dioxide elimination rate, the predicting means including means for selecting a predictive relationship appropriate for the patient, wherein a first predictive relationship is selected for ill patients and wherein a second predictive relationship is selected for healthy patients, and wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases.   
     
     
       53. The system of claim 52, wherein the predicting means includes means for determining the cardiac output of the patient based on the selected predictive relationship and the determined current value of the carbon dioxide elimination rate. 
     
     
       54. A system for determining a cardiac output level of a patient from the carbon dioxide elimination rate of the patient, the system comprising: a flow rate sensor which measures a flow rate of the exhaled gas expired by the patient and which provides a flow signal representative of the flow rate;   a carbon dioxide sensor which senses a carbon dioxide level of the exhaled gas expired by the patient and which provides a carbon dioxide signal representative of the carbon dioxide level;   an input device;   a processor, operatively coupled to the input device, which: receives the carbon dioxide signal and the flow signal;   determines a current value of lung carbon dioxide elimination rate of the patient from the carbon dioxide signal and the flow signal; and   predicts the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate of the patient, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases, wherein a first predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate for ill patients may be selected by an operator via the input device, and wherein a second predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate for for healthy patients may be selected by an operator via the input device, so that the processor uses the selected first or second predictive relationship to predict the cardiac output level of the patient based on the relative respiratory health of the patient.       
     
     
       55. A system for determining a cardiac output level of a patient from the carbon dioxide elimination rate of the patient, the system comprising: a flow rate measurement sensor which measures the flow rate of the exhaled gas expired by the patient and which provides a flow signal representative of that flow rate;   a carbon dioxide sensor which senses the carbon dioxide level of the exhaled gas expired by the patient and which provides a carbon dioxide signal representative of that carbon dioxide level;   an input device;   a first processor which receives the carbon dioxide signal and the flow signal, and determines a current value of the lung carbon dioxide elimination rate of the patient from the carbon dioxide signal and the flow signal and which generates a lung carbon dioxide elimination rate signal representative of the current value of the lung carbon dioxide elimination rate; and   a second processor, operatively coupled to the input device, which receives the lung carbon dioxide elimination rate signal and, based on the current value of that signal, predicts the cardiac output level of the patient, wherein the cardiac output level of the patient predictively increases as the lung carbon dioxide elimination rate of the patient increases, and wherein a predictive relationship of the cardiac output level of the patient as a function of the current value of lung carbon dioxide elimination rate may be selected by an operator via the input device, wherein a first predictive relationship is selected for ill patients and a second predictive relationship is selected for healthy patients, so that the second processor predicts the cardiac output level based on the relative respiratory health of the patient.